I’ve made some progress and it seems that its is related to the connection speed. I managed to simulate this with the chrome developer console and limit the network speed to simulate a mobile connection.
The browser seems to load only a few bytes of the webGL videos and then stops when I’m loading the scene. He then loads further when I start the video, but because it wasnt “fully” loaded in the first place I get a black screen and webGL errors.
So does someone know how I could overcome that behaviour and tell the browser to load the video fully in the background? Maybe when I activate the autoplay feature for the loadvideo puzzle?